Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With rotor
Reexamination Certificate
2002-05-23
2004-10-26
Karlsen, Ernest (Department: 2829)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With rotor
C323S273000, C324S765010
Reexamination Certificate
active
06809511
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to an IC test apparatus (IC tester) and a device power supply used in the test apparatus, and in further detail, to a power supply referred to as an SMU (Source Measure Unit) or DPS (Device Power Supply) that applies voltage and current to and performs measurement on an IC, and a test apparatus that uses the power supply.
2. Discussion of the Background Art
The SMU as shown in Japanese Laid-Open Patent No. Sho 58-121812 has been used in the past as a device power supply for the IC of an IC test apparatus, such as IC testers and DC parametric test systems, etc. By using the SMU, it has been possible to perform function tests on applying voltage to the terminal of the IC while limiting current, or to measure current with applying voltage to the IC test apparatus, with a short settling time.
As shown in
FIG. 1
, device power supply
10
having a negative feedback amplifier according to the prior art, for instance, includes input resistor R
2
14
, amplifier A
1
16
, current detection resistor R
3
18
, inductances L
1
20
, L
2
21
, and L
3
25
, load impedance Z
1
22
, buffer B
1
26
, feedback resistor R
1
28
, capacitor C
1
30
, input terminal
12
and its voltage V
In
, force terminal
52
on the high output-side of the apparatus, sense terminal
54
on the high output-side of the apparatus, and DUT terminal
24
and its voltage V
out
. Load impedance Z
1
22
here includes impedances such as the capacitive components of the termination resistor and by-pass capacitor, capacitive and/or inductive components of filter circuit for eliminating noise, and the impedance of the device under test (DUT). Buffer B
1
26
monitors and buffers the voltage V
out
of DUT terminal
24
. Inductance L
1
20
is an inductance due to the extended cable from one end of R
3
18
, connected to inductance L
1
20
, in the cage of the IC test apparatus on which device power supply
10
is set up, to force terminal
52
on the high output-side of the test head where the DUT is put on. And similarly, inductance L
3
25
is an inductance due to the extended cable from the sense terminal on the high output-side of the test head, to buffer B
1
26
inside the cage. L
2
21
is the inductive component of the filter that has been connected for noise elimination. The output of amplifier A
1
16
is connected to force terminal
52
on the high output-side with R
3
18
and L
1
20
in between. Sense terminal
54
on the high output-side is connected to the inverting input of A
1
16
with L
3
25
, B
1
26
, and R
1
28
in between and makes up part of the negative feedback loop. Force terminals and sense terminals are similarly set up on the low output-side of device power supply
10
in the case of full Kelvin connection (four-terminal connection), but in order to simplify the description, only the grounded terminals are shown in FIG.
1
and the details are omitted.
Voltage V
in
in conjunction with the setting voltage is applied to input terminal
12
. Input terminal
12
is connected to the inverting input of amplifier A
1
16
and therefore, a feedback amplifier is made by the path A
1
-R
3
-L
1
-terminal
52
-L
2
-terminal
24
-terminal
54
-L
3
-B
1
-R
1
-R
2
and the voltage represented by V
out
=−R
1
/R
2
*V
in
is output to DUT terminal
24
.
Suppose that there is no inductance L
1
, L
2
, or L
3
in the cable and the filter circuit as an ideal case in order to consider the transfer characteristics of the entire loop. in the case, it is supposed that load Z
1
is consisted of pure resistive component. There is no phase delay and gain is a value between 0 and 1 in the transfer characteristics from R
3
and Z
1
. Since a circuit consisting of L
3
, B
1
, R
1
, R
2
, C
1
and A
1
make an integrator, the phase delay of their transfer characteristics is 90 degrees. Consequently, the phase delay of the overall transfer characteristics is a maximum of 90 degrees and therefore, the transfer characteristics of the total feedback loop are stable, regardless of the gain of the integrator.
Nevertheless, in actual measurements, if a large current of one ampere (A) or greater is applied to the DUT, very small resistance is used in order to reduce the voltage drop at resistor R
3
18
. Sometimes, inductance L
1
and L
3
due to the extended cable become to be relatively large. An L-C filter can be added in order to reduce various types of noise and therefore, inductance of the L-C filter is added to inductance L
2
21
. Accordingly, the capacitive component of the L-C filter (referred to as Cz) and the capacitive component of the by-pass capacitor are included in Z
1
22
.
In this case, R
3
-L
1
-L
2
-Z
1
becomes the secondary resonant circuit of L-R-C. Moreover, as previously mentioned, since R
3
is small, the quality factor of the secondary resonant circuit is high. As a result, the phase delay of the transfer characteristics from the output of amplifier A
1
16
to DUT terminal
24
has a maximum angle of 180 degrees (when R
3
is 0 &OHgr;.). However, in normal cases, R
3
is not at 0 &OHgr; and therefore, it becomes 140 degrees for instance.
Next, the transfer characteristics from DUT terminal
24
to the output of buffer B
1
26
will be considered. The effects of inductance L
3
25
can be disregarded because the input impedance of buffer B
1
26
is high and therefore, as in the case where there is no inductance L
3
25
, the transfer characteristics become a gain of 1 and a phase delay of 0 degrees. The transfer characteristics from the output of buffer B
1
26
to the output of amplifier A
1
16
become integration characteristics and the phase delay becomes 90 degrees.
As a result, the phase delay angle of overall transfer characteristics is a maximum of 270 degrees (when R
3
is 0 &OHgr;). And if the gain of the overall transfer characteristics become 0 dB or higher at the frequency where phase delay is over 180 degrees, oscillation will occur. However, in most cases, R
3
is not 0 &OHgr; and the phase delay becomes smaller than 180 degrees, therefore, oscillation does not occur, but ringing can occur because of the less phase margin.
As previously mentioned, there are problems with conventional device power supplies in that oscillation or ringing readily occurs, when the capacitive component of load Z
1
is large. Once oscillation or ringing have occurred, a higher voltage than the maximum allowable voltage can be applied to the power source terminals of the device, then, the device itself will be damaged. The device can also break down. Moreover, as a result of the ringing, etc., a good device can also be evaluated as a defective one.
Furthermore, the power current has increased with the recent increase in speed and reduction in operating voltage of the IC and therefore, resistance R
3
18
tends to be lower. Therefore, it becomes necessary to prevent oscillation and ringing of device power supplies.
SUMMARY OF THE INVENTION
In light of these problems of the prior art, the present invention provides a device power supply and IC test apparatus with which there is little oscillation, even if the load capacitive component is large, with the short stabilizing time remaining uncompromised to the utmost during IC tests.
The present invention presents a device power supply, having an amplifier, a high output-side force terminal connected to the output of the amplifier, a high output-side sense terminal, and a first feedback circuit from the high output-side sense terminal to the input of the amplifier, where a first low-pass filter is placed between the amplifier output and the first feedback circuit. Moreover, there is a first inductance between the first low-pass filter and the high output-side force terminal. By means of this type of structure, oscillations rarely occur, even under a load with a large volume component.
Moreover, the first low-pass filter can have a capacitor that connects the amplifier output and the first feedback circuit and a resistor inserted in series between the capacitor connection terminal of the first feedba
Agilent Technologies , Inc
Karlsen Ernest
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